Starrett 831A Small Hole Gage .125-.200"/3.2-5.1mm 2-13/16"/70mm Length

The Starrett 831 Series Small Hole Gages are well balanced tools that are ideal for accurately measuring small holes, slots, grooves and recesses in all kinds of work. They all feature a hardened-ball measuring surface with two-point contact, the radius on each gage is less than the minimum diameter to be measured, which provides the two-point contact necessary for maximum accuracy. All have a smooth, sensitive adjustment for better feel, giving more accurate measurements and the adjustment of the gage beyond their Range is restricted by a safety stop that prevents breakage. Accurate measurements are obtained by slightly "rocking" these gages in the hole to be measured. This will guarantee contact at the true diameter. The final size is then obtained by measuring over the ball contacts with a micrometer. This model has a measuring Range of .125-.200" / 3.2-5.1mm and is approximately 2-13/16" / 70mm in length. This series permits use in even the most shallow holes, slots and recesses due to the half-ball, flat bottom gaging surface.